1. Field of the Invention
The present invention relates to a method for forming a pattern of a liquid crystal display device, and more particularly, to a method for forming a pattern of a liquid crystal display device using a microtransfer method, a non-photolithography method, and a method for fabricating a thin film transistor array substrate of a liquid crystal display device using the same.
2. Description of the Related Art
As the interest in an information display and the demand for a portable information media increase, researches on a light flat panel display (FPD) substituting for a cathode ray tube (CRT) are preponderantly ongoing. Particularly, a liquid crystal display device of such flat panel displays is a device for displaying an image using optical anisotropy of a liquid crystal and is being actively used for a notebook computer or a desktop monitor because of its excellent resolution, color display and image quality.
A general liquid crystal display device displays an image by controlling the light transmittance of a liquid crystal by using an electric field. To this end, a liquid crystal display device largely includes a color filter substrate, an array substrate and a liquid crystal layer formed between the color filter substrate and the array substrate.
FIG. 1 is a partial plan view of one pixel region of an array substrate for a liquid crystal display device according to a related art. It is known that the array substrate has a plurality of such pixel regions.
In FIG. 1, the array substrate 10 includes a pixel electrode 18 formed on a pixel region, a gate line 16 and a data line 17 arranged horizontally and vertically on the substrate 10, and a thin film transistor (TFT) 20 (a switching element) formed at an intersection of the gate line 16 and the data line 17.
The thin film transistor 20 includes a gate electrode 21 connected to the gate line 16, a source electrode 22 connected to the data line 17 and a drain electrode 23 connected to the pixel electrode 18. The thin film transistor 20 includes a first insulating film (not shown) for insulating the source/drain electrode 22, 23 and an active layer 24 forming a conductive channel between the source electrode 22 and the drain electrode 23 by a gate voltage supplied to the gate electrode 21. In addition, a second insulating film (not shown) having a contact hole 26 is formed on the drain electrode 23, so that the drain electrode 23 and the pixel electrode 18 are electrically connected through the contact hole 26.
Here, the pixel region means an image-displayed region defined by the intersection of the gate line 16 and the data line 17. The pixel electrode 18 formed on the pixel region is made of a transparent conductive material having excellent light transmittance, such as Indium Tin Oxide (ITO).
The array substrate constructed as above constitutes a liquid crystal display panel by being attached to the color filter substrate by a sealant, and the attachment of these two substrates is made through an attachment key formed at the array substrate or the color filter substrate.
Meanwhile, in fabricating a liquid crystal display, a plurality of mask processes (i.e., photolithography process) are needed to fabricate an array substrate including thin film transistors. Therefore, in order to improve productivity, a method for reducing the number of mask processes is required.
Hereinafter, a process for fabricating a general liquid crystal display device will now be described in detail with reference to FIGS. 2A to 2G.
FIGS. 2A to 2G are flow charts showing a fabrication process of a liquid crystal display device shown in FIG. 1, and particularly, a fabrication process of an array substrate including a thin film transistor is shown.
First, as shown in FIG. 2A, a gate electrode 21 is formed on a substrate 10 made of a transparent insulating material such as glass. The gate electrode 21 is formed such that gate metal is deposited at the entire surface of the substrate 10, which then passes through a photolithography process.
Then, as shown in FIG. 2B, a first insulating film 15a which is a gate insulating film, an amorphous silicon thin film 24a and an n+ amorphous silicon thin film 25 are deposited at the entire surface of the substrate on which the gate electrode 21 is formed in turn. The amorphous silicon thin film 24a is patterned to be used as an active layer of the thin film transistor, and the n+ amorphous silicon thin film 25 is formed for ohmic-contact between the source/drain electrodes and source/drain regions of the active layer.
Then, as shown in FIG. 2C, the first insulating film 15a, the amorphous silicon thin film 24a and the n+ amorphous silicon thin film 25 are patterned through a photolithography process, thereby forming a gate insulating film 15 pattern, an active pattern 24, and a patterned film 25.
Thereafter, as shown in FIG. 2D, a conductive metal 30 for forming source/drain electrodes is deposited at the entire surface of the substrate 10.
Next, as shown in FIG. 2E, the conductive metal 30 is patterned through a photolithography process, thereby forming a source electrode 22 and a drain electrode 23. Here, the conductive metal 30 and the n+ amorphous silicon thin film 25 are completely removed except for their portions corresponding to the source/drain electrodes 22, 23 patterns.
Next, as shown in FIG. 2F, a second insulating film 15b is deposited at the entire surface of the substrate 10, and then a contact hole 26 exposing a part of the drain electrode 23 is formed through a photolithography process.
Lastly, as shown in FIG. 2G, a transparent conductive material such as Indium Tin Oxide (ITO) is deposited at the entire surface of the substrate 10 on which the second insulating film 15b is formed, and then a pixel electrode 18 connected to the drain electrode 23 through the contact hole 26 is formed through a photolithography process.
As discussed above, in order to fabricate such a liquid crystal display device, several deposition processes and photolithography processes have to be performed. Particularly, in fabricating an array substrate including a thin film transistor array as described above, a plurality of photolithography processes are required to form a gate electrode, an active pattern, a source/drain electrodes, a contact hole and a pixel electrode.
The photolithography technology includes a plurality of complex processes, such as the application of photosensitive material, alignment, exposure, development or the like as a series of processes for forming a desired pattern by transcribing a pattern drawn on a mask onto a substrate where a thin film is deposited.
In the exposure process, a mask is disposed at a proper position, align keys of the mask and the substrate are aligned, and then a light source is radiated. Here, however, because of the limitation of the exposure equipment, it is difficult to make the accurate alignment. Accordingly, there is a limit to forming a fine pattern which requires high precision, and productivity is deteriorated since a plurality of photolithography process need to be repeated.
In addition, since a mask designed to form a pattern is very expensive, as the number of masks used during the process is increased, the fabrication cost of a liquid crystal display device is increased in proportion to the increased number of masks.